It is already known for the injection valves of a fuel injection system to be actuated such that they are opened and closed again as exactly as possible at predefined points in time in order to inject as accurately as possible a predefined quantity of a pressurized fuel into a cylinder of the internal combustion engine. In this way, and possibly also by means of additional pre- and/or post-injections in addition to a main injection within an injection cycle, the efficiency of the internal combustion engine can be increased, and exhaust-gas and noise emissions can simultaneously be reduced.
An injection valve, commonly also referred to as injector, has a closure element which can be moved by means of a drive for the opening and closing of the injector. In the closed state of the injector, in which no injection is performed, the closure element is situated in a closed position, in which it closes all of the injection openings of the injector. By means of the drive, the closure element can be lifted proceeding from its closed position, in order to thereby open up at least some of the injection openings and initiate the injection.
The closure element commonly has, or is commonly designed as, a nozzle needle. In its closed position, said nozzle needle is seated on a needle seat of the injector. The drive of the injector comprises, for moving the closure element, an actuator which is designed to, in a manner dependent on a control signal, lift the closure element out of the closed position to a stroke height, hold said closure element at said stroke height, and/or move the closure element back into the closed position. For example, said actuator may be provided by a piezo element, which expands or contracts owing to electrical charging or discharging processes and thereby initiates a stroke or closing movement of the closure element. Such actuators, also referred to as piezo actuators, are particularly highly suitable for precise and delay-free movement of the closure element. This is the case in particular with so-called directly driven piezo injectors, in the case of which a direct and delay-free transmission of force between the piezo actuator and the closure element is made possible.
DE 10 2011 075 732 A1 has disclosed a regulation method for an injection valve and an injection system. In said known method, in repeating injection cycles and in a manner dependent on a setpoint stroke height of a closure element of the injection valve, in each case at least one control signal for actuating a drive of the injection valve is generated, wherein the drive is actuated by means of the control signal for lifting the closure element to the setpoint stroke height, and the closure element is lifted by means of the drive to an actual stroke height, wherein at least one measurement variable which correlates with the actual stroke height is detected, and the actual stroke height is determined in a manner dependent on said at least one measurement variable, wherein the control signal is generated, in at least one of the subsequent injection cycles, in a manner dependent on a deviation of the actual stroke height from the setpoint stroke height.